Keith's Hortons (plural, the one he flies now is not the original from the '90's) have had clear plastic fins to provide the needed stability. I asked him specifically about the exhaust extensions being used on the Wingsontheweb 229 and he said in his opinion the extensions are acting as fins and the stability they provide is not from any effect they might have on the fan airflow.

but the exhaust extensions are simply allowing the efflux to exit after the airframe. to me, that means it's adding stability in the same way it does on the vulcan. I'm not saying that these tubes don't add directional stability, but the fact still remains that there are aero issues without the tubes and then virtually no aero issues with them attached. that speaks volumes right there, especially considering there are no aero issues associated with flying the Vulcan.

Well how do you explain that 2 identical Ho229's one powered by turbines and the other by edf units behave differently. I have now flown my turbine powered Horten without the extensions without a problem. There is video of the edf powered one getting completely unstable. The position of the intakes is a red herring and comparisons with an Avro Vulcan are irrelevant. I have had 2 Dh108 both turbine powered and both very good flyers, again irrelevant as they have fins.

I've seen turbine powered ones fly with no problems, and EDF versions fly with all the aero problems that are discussed. the guy that flew the turbine had some resoning as to why it doesn't cause the same issues and I personally agree with them......................

turbines are much like a high powered jet of air coming out of a nozzle in a mechanics shop. the efflux is a very high powered, straight and focused columb of air, that has very little (if no) time to interact with the center section. it loses its energy very fast, but not till well after it is past the airframe. conversly, in an EDF it is a very wide, slow moving and tubulent (twisting) columb of air that has all the time in the world to mix with the air flowing over the center section of the wing. the fact that it's swirling does very little to help the situation, when compared against the turbine, who's efflux columb is straight as an arrow, with no swirl whatsoever.

the intakes on a Vulcan are indeed relevant. the only difference between the 229 and the Vulcan, is that there is a small part of the fuselage ahead of the intakes on the Vulcan. however, the freestream does not see this and only sees the wing, so it is very much relevant. vertical fins are actually irrelevant, because the real versions and the turbine versions fly just fine without them. noone even mentioned vertical fins except you, since we know that they aren't needed for directional stability. the full size and the versions that fly just fine prove this without a doubt.

but the exhaust extensions are simply allowing the efflux to exit after the airframe. to me, that means it's adding stability in the same way it does on the vulcan. I'm not saying that these tubes don't add directional stability, but the fact still remains that there are aero issues without the tubes and then virtually no aero issues with them attached. that speaks volumes right there, especially considering there are no aero issues associated with flying the Vulcan.

I don't know what the answer is, I'm just passing along a bit of insight to Keith's Hortons and the conversation he and I had a year or two ago about the extensions.

hey Mark. I'm not saying you, or anyone else is wrong, by any means. all we all know for certain, is that there's something wrong with the Horton under EDF power that doesn't exist with turbine versions. and we all know that these extensions fix the problem. I think we all agree on that point, correct!?

to me though, the extensions are kinda like a bandaid fix. they are fixing an aero issue, without actually finding out the cause of it. this topic actually intrigues me, because noone has yet to find a deffinitive answer and is merely speculation by a great many minds. I think Thomas is onto something though, especially since he intends to test the theories. I'd really love to see if my vent theory works.

Mark,
Thank you for passing on Keith's thoughts! Its a very logical straight forward explanation. The edf is producing some issues but no one really knows what they are. The lateral stability added by the tubes may very likely be the actual fix to the unknown cause.

The Northrop YB-35 (prop version) benefited from lateral stability added by the drive shaft pylons. On the YB-49 (jet version) Jack Northrop wasn't happy but he had no choice but to add 4 small vertical fins to provide the stability lost by the lack of those drive shaft pylons on the YB-35. Seems like the extended thrust tubes are providing the same result!

Regarding the slots back by the exhaust area on the full size aircraft, there is a book titled "Horten Ho 229 Spirit of Thuringia". On page 61 they discuss some of the details of the 8-229 V3 (mind you, V2 was the only jet version that flew). Anyway, back to page 61, they discuss how the new Jumo 104-004B turbojets would allow them to change back to the original 13% wing thickness and along with the built in bleed air nozzle cooling system of the Jumo 004B, the flush mounted steel plates aft of the exhaust were to be cooled by air fed from the lower surface of the wing.

I'm sure you guys have seen this before,but it shows it can be done.
Btw,from what I've read,mostly HerkS work,the props themselves provided most of the stability on the Northrop designs,acting as a vertical surface.
Regards Stuart

so, they were vents that drew air from the lower surface!!!??? so I was on the right track then.........sort of. perhaps this could be used for my idea of creating a cushion for the EDF efflux, so it doesn't interfere with the aerodynamics of the wing. just a thought of course.